1. Field of the Invention
The present invention relates to a rotational angle detecting apparatus and a torque detecting apparatus used in a steering apparatus, in which a first shaft connected with a steering member and a second shaft connected with a steering mechanism are connected with each other by a connection shaft, a rotor provided with one or a plurality of targets is coaxially provided at each of the first shaft and the second shaft, two detecting means disposed opposite to each target output detection signals having phases different from each other in accordance with each position of the target as the rotor rotates, a steering torque applied to the first shaft is detected on the basis of the detection signals respectively outputted from the detecting means and steering is assisted in accordance with the detected steering torque.
2. Description of Related Art
Known as one of steering apparatuses for automobiles is an electric power steering apparatus capable of reducing driver's load by driving an electric motor to assist steering. Such an electric power steering apparatus comprises an input shaft joined to a steering member (steering wheel), an output shaft connected to steerable wheels by a pinion and a rack or the like and a connection shaft for connecting the input shaft with the output shaft so as to detect, by a torque sensor, a steering torque applied to the input shaft on the basis of an angle of torsion generated at the connection shaft and to drive an electric motor for steering assist, which interlocks with the output shaft, in a controlled manner on the basis of the steering torque detected by the torque sensor.
The present applicant has suggested in Japanese Patent Application No. 2002-69121 a rotational angle detecting apparatus comprising one or a plurality of first targets provided at a rotor; first detecting means, disposed opposite to the first targets, for outputting a detection signal as the rotor rotates; second detecting means for outputting a detection signal having a phase different from that of the detection signal outputted from the first detecting means; second targets, provided at a rotor, the number of which is coprime with the number of the first targets; third detecting means, disposed opposite to the second targets, for outputting a detection signal as the rotor rotates; and fourth detecting means for outputting a detection signal having a phase different from that of the detection signal outputted from the third detecting means, wherein a rotational angle of the rotor is detected on the basis of the detection signals respectively outputted from the first detecting means, second detecting means, third detecting means and fourth detecting means. The application also suggests a torque detecting apparatus (torque sensor) comprising this rotational angle detecting apparatus and a steering apparatus comprising this torque detecting apparatus.
According to the conventional electric power steering apparatus, a steering assist operation stops when a malfunction is detected in the torque sensor. As a result, when a malfunction occurs in a torque sensor while the automobile is running, the malfunction prevents the driver from driving comfortably, without notifying the driver of what has happened. In a worst situation, there may arise a problem that resistance to the steering wheel increases while the automobile is running, it becomes impossible to operate the steering wheel appropriately and thereby it becomes impossible to move the vehicle for emergency evacuation.